Figure 2
Effect of D 4 receptor on insulin-mediated proliferation in A10 cells. A. Effect of insulin on the proliferation of A10 cells. A10 cell proliferation was determined by the uptake of the tetrazolium salt, 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) after incubation with different concentrations of insulin. Results are expressed as MTT optical density (n = 10, *P < 0.05 vs. control, one-way ANOVA, Holm-Sidak test). Control cells were treated with vehicle. B. Effect of D4 receptor agonist on the proliferation of A10 cells. A10 cell proliferation was determined by MTT after incubation with the indicated concentrations of the D4 receptor agonist PD168077 (10-10 mol/L~10-6 mol/L). Results are expressed as MTT optical density (n = 10, P = NS, one-way ANOVA, Holm-Sidak test). Control cells were treated with vehicle. C and D. Effect of D4 receptor on insulin-mediated proliferation in A10 cells. A10 cell proliferation was determined by MTT (C) or number of cells (D) after incubation with insulin (10-7 mol/L) in the absence or presence of varying concentrations of the D4 receptor agonist, PD168077 (PD, 10-11 mol/L - 10-6 mol/L). Results are expressed as MTT optical density or cell number/well (n = 8-9, *P < 0.05 vs. control; #P < 0.05 vs. insulin alone). E-G. The specificity of D4 receptor action on proliferation of A10 cells. A10 cells were incubated with vehicle (control), insulin 10-7 mol/L alone or in the presence of the D4 receptor agonist, (PD, PD168077, 10-7 mol/L) (insulin + PD) or both D4 receptor agonist (PD) and D4 receptor antagonist (L, L745870, 10-7 mol/L) (insulin + PD + L) for 24 hours. A10 cell proliferation was determined by MTT (E) or [3H]-thymidine incorporation (F) and number of cells (G). Results are expressed as MTT optical density (n = 8) or cpm/mg protein (n = 4) 0r cell number/well (n = 9; *P < 0.05 vs. control; #P < 0.05 vs. insulin alone).